Potentiometer



Jan. 23, 1968 l D, D, HlLLMAN 3,365,691

POTENTIOMETER Filed NOV. 29, 1966 30 75 '26d 34p LIMZZ 3,365,69i Patented dan. 23, 1968 3,365,691 POTEN'IIMETER Darrel D. Hillman, Orange, Calif., assigner to Bourne, Inc., a corporation of California Filed Nov. 29, 1966, Ser. No. 597,671 5 Claims. (Cl. 338-183) ABSTRACT F THE DISCLUSURE The invention resides in a very small high-quality inexpensive potentiometer of the type in which adjustment is effected by rotation of a leadscrew. The potentiometer is characterized by ability to operate satisfactorily at exceptionally high temperature, by comprising only a very small number of parts all of which are inexpensive, and by exceptionally small size, a typical representative specimen being of the order of 12.7 mm. long, 2.5 mm. wide, and 3.2 mm. high. Also the potentiometer is characterized by ability to be overdriven without adverse eiiects, and by excellent resistance to adverse environmental conditions such as high humidity. The potentiometer comprises an elongate molded box-like body, a recessed ceramic cover of elongate plate-like form carrying sealed terminal members and applied strips or stripes of conductive and resistive material connected to terminal members and forming a resistance element and return conductor, a one-piece sliding conductive contact device brushing on the conductive and resistive stripes and disposed upon and driven by a ceramic leadscrew that is borne by the body and is retained in place in the body by a retainer. Seal means insure resistance to ingress of moisture and lother foreign material.

It is a primary objective of the invention to provide a very small leadscrew-adjusted potentiometer of inexpensive construction which is capable of satisfactory operation under adverse environmental condiions of high temperature and high humidity and capable of being overdriven in either direction without adverse effects.

Another object of the invention is to provide improvements in the combination of a leadscrew contact device driven by the leadscrew, and resistive and conductive means brushed by the contact device during adjustment of a potentiometer.

Another object of the invention is to provide a simple and satisfactory leadscrew-adjusted potentiometer of very small size of the order of fourteen millimeters length.

Other objects and advantages of the invention will hereinafter be set out or made evident in the appended claims and the following description of a preferred embodiment of potentiometer incorporating the invention, the description having references to the accompanying drawings illustrating details of the potentiometer.

In the drawings:

FIGURE 1 is a pictorial view of the preferred embodiment of potentiometer incorporating the invention;

FIGURE 2 is a transverse sectional view of the notentiometer, on a much large scale than FIGURE l, showing details of the relative arrangement of the leadscrew, contact device or slider, and resistive and conductive stripes, of the potentiometer;

FIGURE 3 is a longitudinal sectional view, with some parts not sectioned showing characteristics of the leadscrew and its relationship to the body and other parts of the potentiometer;

FIGURE 4 is a plan view of a cover member forming part of the potentiometer housing with potentiometer components mounted thereon; and

FIGURE 5 is a view of a metal alloy blank from which a conductive contact or slider device is formed.

Referring first to FIGURES l land 3, the potentiometer, denoted generally by numeral 16, comprises an elongate housing l2 of box-like form, the housing comprising essentially an elongate open base 14 and a cover 15. The base 14 is formed by molding, or insulation material such as ceramic or synthetic resin or resin and filler, capable of enduring long exposure to high temperature without significant or objectionable degradation or deterioration. Of satisfactory ceramic materials, steatite and alumina may be noted; and of suitable other materials, diallyl phthalate (with or without filler such as asbestos) may be noted. The base is formed with a cavity between end walls 14W, 14W', which cavity is located and arranged to be closed by the cover l5. The base is formed with ledges 14m, 14m (FIGURE 3) on the end Walls and ledges 14n, 14n (FIGURE 2) on the side Walls, on which ledges cover 15 is arranged to rest and to be sealed around its periphery to the base. The base is provided, at the interior of end wall 14W, with a preferably circular recess 141' which is -dimensioned and arranged to pr-ovide a bearing for the inner threadless end portion 161' of a leadscrew 16. The opposite end wall 14W of the potentiometer base is provided with a stepped bore 14b through which the threadless head end portion of the leadscrew 16 extends and which bore provides a second bearing for rotational support of the leadscrew. The two bearings are accordingly tor-med in coaxial relationship, preferably during the molding operation.

The leadscrew 16 is formed of strong rigid insulation, such as alumina or like ceramic material, and as a onepiece actuator for the movable contact device used to interconnect a selected point of a resistance element with conductor means. The leadscrew is formed with a head 16h arranged and constructed for coaction with a driving tool, such as a screwdriver, whereby manual or mechanical rotation of the screw is facilitated. The head end portion of the leadscrew includes a threadless shank 16s, the cylindrical surface of which is interrupted by an annular retainer-clip groove 16g and also by an annular O-ring `groove 161'. Groove 16g is disposed and arranged to be positioned to accommodate a slightly bowed U-shaped resilient wire retainer `device or clip 18 which straddles the leadscrew and the legs of which device ride in the groove and bear against the inner face of end wall 14W' when the leadscrew is in normal position `as depicted in FIGURE 2. Groove 1dr is formed and arranged to accommodate an O-rin-g seal 20 in the counterbore or outer portion of bore leb, as shown in FIGURE 2. Thus by the described means the leadscrew is disposed for rotation about its axis and is restrained from axial translation relative to the base 14, and the bore 14b is sealed against undesired passage of material.

The open face of box-like base 14 is arranged, as noted, to be closed by cover 15 whereby an elongate enclosed chamber is provided. The cover, as noted, is of insulation, and as indicated in FIGURE 4 supports on its inner exposed face an elongate resistance element 22 of conventional material, but preferably a cermet element formed in situ on the cover. The resistance element is provided with conductive metal terminations 22t, 22t at its ends, the terminations comprising strips or lms contacting respective areal extents of the element and in electrical Contact with respective terminal pins 22p, 22p. The terminations may be applied films or strips of gold, platinum or the like. Further, cover 15 supports on its inner face, generally parallel to resistance element 22, a return or collector conductor 24 of strip or metal-stripe form. The collector conductor is electrically connected, by physical contact, with a terminal pin 24p. The terminal pins 22p, 22p and 24p extend through and are sealed around their respective peripheries to cover 15, the sealing being such as to prohibit passage of material along the surface of either pin from the exterior of the cover to the interior chamber of the housing.

Disposed on leadscrew 16 within the elongate chamber C in the box-like base 14 is a contact member or device 26 composed of a single piece of metal or conductive resilient alloy, initially of the character of a flat shaped member punched from a flat sheet and of the form indicated at 26 in FIGURE 5. As indicated in the latter drawing, the contact device is initially formed to have first and second generally rectangular side portions or limbs, 26u and 26v, separated by a central portion 26W from which extend first and second contact fingers e and 26e. The latter finger preferably is bifurcated as shown. A portion of the material of the sheet 26 is removed by punching or the like to leave an opening 260 into which extends a dog 26d formed by a shaped portion of the sheet.

The contact device 26 is formed from the fiat punched sheet indicated in FIGURE 5, by turning up into opposed jaws 26W and 26]'v (FIGURE 2) the limbs 26u and 26V, respectively, turning down and back, in opposite directions, the contact fingers 26e and 26C as shown in FIG- URE 3, and turning up dog 26d into position between the jaws, as indicated in FIGURES 2 and 3. As thus formed, the contact device permits the leadscrew to be turned into the device, and When that is done, it clasps or grips a short section of the leadscrew between the jaws l2612's and 26jv, the central portion 26W being thus brought up into contact with the leadscrew. Further, when thus mounted on the leadscrew as the latter is pressed into place in base 14, the contact device is disposed with contact fingers 26e and 26C positioned to come into brushing electrical engagement with the resistance element 22 and the return conductor 24, respectively, and the corner junctures formed at the lines of juncture of jaws 26m and 26]'v are disposed to bear lightly against the side walls of the chamber to aid in preventing rotation of the device on the leadescrew. As is made evident in FIG- URES 2 and 3, the tab or dog 26d which is struck up from the body of the contact device is disposed to normally ride in the groove 16g of the square thread of the leadscrew, between adjacent convolutions of the land 162i of the thread. The fully formed contact device is assembled with the leadscrew by first inserting the inner end 161' of the screw through bore Mb of base 14, then turning or pressing the end portion of the screw between the jaws of the slider while holding the tab or dog 26d out to clear the screw until the latter is fully seated between the jaws of the contact device. Preferably the arrangement is such that continued movement of the screw into position in the potentiometer base either causes the slider to move into a position in which the dog either springs into the groove of the thread or will enter the groove incident to rotation of the leadscrew. Otherwise the contact device is moved manually into thread-engaging position.

With the contact device 26 and the lO-ring seal 20 assembled on the leadscrew and the latter pressed into place in the base 14, and with the retainer clip 18 pressed home and preventing longitudinal movement of the screw relative to base 14, mechanical operation of the slider or contact device 26 by leadscrew rotation can be checked with visual monitoring. The ends of the square-thread groove 16g of the leadscrew are formed as cam-like inclines extending from the smooth cylindrical surface of the adjacent end portions of the leadscrew down to the full depth of the groove, as indicated in FIGURE 3. Further, the dimensioning is such that incident to continued rotation of the screw in either direction, the interengaging dog and thread will cause the contact device to be driven to the end of the thread of the screw and then dog 26d to be resiliently cammed out of the respective end of the groove and onto the adjacent cylindrical surface of the screw, from which disposition or position it can, once each revolution of the screw, snap or enter into the end of the groove. Alternatively, when thus cammed out of the groove 16g, reversal of the direction of rotation of the leadscrew causes the stressed resilient dog 26d to ride down the inclined or cam surface end portion of the groove of the thread and to thus be re-engaged with the land or side wall of the groove of the thread. Thus rotation of the leadscrew causes traverse of the contact device along the leadscrew in either direction according to the direction of the rotation. As is evident, continued rotation of the leadscrew to excess in either direction results in the driving dog 26d of the contact device riding out of the groove of the thread and thus effectively disengaging the cooperating driving connection between the leadscrew and the contact device and permitting continued overdriving of the leadscrew without any resultant arm to the potentiometer. That is, in effect the contact device 26 is de-clutched from the leadscrew, although still secured to it.

Following mechanical testing of the driving leadscrew and driven contact device, the cover 15 of the potentiometer housing is applied, the resistance element 22 and the conductor 24 engaging respective ones of the contacts 26e and 26C and slightly stressing the latter members as the cover is pressed home onto the aforementioned shelves provided on the inner walls of the base 14. Sealant, such as high-temperature synthetic resin, or ceramic cement, is used to seal the cover 15 to base 14 and to provide the sealed chamber C (FIGURE 3) in the interior of the housing in which `chamber the operating components are protected. Additional protection against ingress of foreign material is preferably provided by filling with potting cornpound or ceramic sealer the shallow external cavity provided beyond coverylS by the side and end walls of base 14, as indicated at 30 in FIGURES 2 and 3. This can be done by applying a resin preform over the terminal pins and applying thereto heat and pressure.

Thus is provided an inexpensive very small leadscrewadjusted potentiometer of superior characteristics and ability to successfully endure physical abuse and usually high temperatures. It is evident that the disclosed potentiometer fully anticipates the aforenoted objects. Due to the very small dimensions of the potentiometer (of the order of one-half inch length) and the consequently small components, the entire contact device may be inexpensively formed of corrosion-proof precious metal or alloy such as that marketed under the trade name Paliney, or Wilkinson Alloy 1651. Also the housing may be formed of relatively expensive material without appreciably increasing the cost over that involved when cheap material is used. By virtue of the small dimensions and the permitted use of high-temperature-resistance material, coupled with the simplicity of the construction, the potentiometer is both inexpensive and capable of successfully withstanding longterm usage in very adverse high-temperature environments. In the light of the disclosure, changes and modifications within the true spirit and scope of the invention will occur to others and hence it is desired that the scope of the invention be not restricted to details of the preferred embodiment except as such restrictions are defined in the appended claims.

I claim: 1. A leadscrew-adjusted potentiometer comprising: first means, including an elongate box-like housing providing an elongate enclosed chamber bounded by end walls one of which has a bore therethrough;

second means, including an insulation leadscrew supported by said housing and extending through said bore and rotatable therein, said leadscrew having a threaded portion bounded at either end by a respective threadless portion disposed in said chamber;

third means, including an elongate resistance element of thin at strip form, supported by said first means and having an exposed surface in said chamber, and terminal means therefor;

fourth means, including an elongate return conductor supported by said first means With a surface exposed in said chamber and disposed generally parallel to said resistance element, and terminal means for said conductor;

and fifth means, including an integral resilientfmetal contact device of flat sheet material having two elongate opposed jaw portions interconnected by an intermediate portion, said jaw portions each extending over a plurality of convolutions of the thread of said leadscrew and supported thereby on said leadscrew, said contact device further having a dog disposed to engage in the groove of the thread of said leadscrew and to ride outwardly from the groove onto either of said threadless portions of said leadscrew incident to overdrive of the latter in respective ones of opposite directions of rotation, said contact device further having first and second elongate contacts each arrange-d to brush on a respective one of said element and said conductor incident to traverse of the contact device by rotation of said leadscrew;

and sixth means, including means for sealing said chamber against ingress of foreign material.

2. A potentiometer according to claim 1, in which said leadscrew is of ceramic alumina composition.

3. A potentiometer according to claim 1, in which said housing is composed essentially of a first insulation member on which said leadscrew is Supported and a second member of ceramic composition upon which said resistance element and said return conductor are supported.

4. A potentiometer according to claim 1, in which said leadscrew is of ceramic material comprising 96% alumina and comprises a lsquare thread, in which potentiometer said housing consits essentially of a box-like structure of insulation and a cover of ceramic material, and in which potentiometer said contact device is of precious-metal alloy.

5. A leadscrew-adjusted potentiometer comprising:

first means, including an elongate boxlike housing structure of insulation providing an elongate enclosed chamber, said housing having a bore through one end thereof;

second means, supported by said first means and including a resistance element having an elongate surface exposed in said chamber, and conductive means including terminal means extending from said element to the exterior of said housing;

third means, including an elongate ceramic leadscrew having first and second threadless end portions and an intermediate threaded portion and the first of said end portions journaled in said bore and the second thereof journaled in a bearing provided by said first means, and said leadscrew having part of each of said threadless portions thereof disposed within said chamber inwardly of the ends of the chamber; and

fourth means, consisting essentially of a unitary contact device composed of a single deformed sheet-like metal member having an elongate intermediate portion and elongate opposed jaw portions extending from respective sides of said intermediate portion, said jaw portions and said intermediate portion each extending along a portion of said leadscrew in said chamber and each engaging a plurality of convolutions of the thread thereof to mount the device on the leadscrew for longitudinal traverse therealong, said contact device further including a resilient dog arranged to engage in the groove of the thread of said leadscrew to cause the device to be traversed along the leadscrew incident to rotation of the latter with the dog so engaged, the -groove of the thread of said leadscrew terminating at each end in a respective inclined cam surface effective to cam said resilient dog outwardly onto a respective threadless portion of the leadscrew incident to excessive rotation of the latter and to permit resilient return of said dog into said groove incident to subsequent reversal of rotation of said leadscrew, said contact device further having contact means brushing on said resistance element and said conductor to electrically interconnect those members, said contact device having `cooperative engagement with at least one of said first and second means to prevent rotation of said contact device with said leadscrew.

References Cited UNITED STATES PATENTS 2,895,116 7/1959 Morrison 338-180 2,962,682 11/19-60 Watley 338-183 2,982,931 5/1961 Elliott 338-183 2,987,688 6/1961 Kopaczek 338--183 ROBERT K. SCHAEFER, Primary Examiner. H. J. HOHAUSER, Assistant Brandner.`

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,365,691 January 23, 1968 Darrel D. Hillman It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line l6, for "arm" read harm line 39, for "usually" read unusually Column 5, line 33, for "consits" read consists Signed and sealed this 4th day of March 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

